1. Field of the Invention
The present invention relates to testing user terminal status and, more particularly, to a network system and method of testing user terminal status to acquire the link status of a wired/wireless terminal associated with a Voice-over-Internet Protocol (VoIP)-based network.
2. Description of the Related Art
Voice-over-IP (VoIP), represented by an Internet Phone, is advantageous to integrally support voice and various multimedia services as well as to provide low cost voice communication service. Furthermore, the VoIP is of importance because it is considered as a core technology for integrating various network technologies into the All IP network using the Internet Protocol (IP).
Most presently commercialized VoIP systems are implemented using a signaling protocol H.323 of the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T). However, H.323 has many problems with respect to expandability and integrality and is difficult implement due to its complexity, since H.323 has been proposed for implementing the video conference system in a Local Area Network (LAN) environment on which the service quality is not secured.
Session Initiation Protocol (SIP), proposed for activating and terminating a multimedia session, is advantageous since it has low implementation complexity and an improved service expandability and integrality, and was conceived in consideration of the Internet, whereby it can accommodate the various multimedia services on the Internet.
SIP is a protocol for easily inviting a counterpart during a video conference or telephone communication rather than controlling the users of the video conference or telephone communication. SIP is not limited to a certain protocol stack but is defined on the basis of a text such as the Hyper Text Transfer Protocol (HTTP), such that it is easy to expand its utilization. SIP can use the conventional e-mail address and provide mobility using a location positioning message such that it is possible to receive the call at the positioned location.
Typical VoIP system uses SIP as the signaling protocol and RealTime Protocol (RTP) for transmitting voice traffic. Also, User Datagram Protocol (UDP) is used as the transmission protocol for transmitting the SIP message and RTP packets. By utilizing the UDP which provide a connectionless service, it is possible to reduce the time for setup of the connection, which is required in the transmission control protocol providing connection-oriented service, resulting in a reduction of the call setup time.
A VoIP terminal based on SIP uses SIP for call processing messages of voice communication between the terminals, and a soft switch, which processes the SIP call processing message, manages the communication between the VoIP terminals. The soft switch knows the terminal number, IP address, and call state information of a VoIP terminal, and provides functions for establishing a link to the counterpart terminal using at least one of a Register message, an Invite message, a Bye message, an Ack message, a Cancel message, and an Options message, etc. The Invite message is used by the terminal for requesting the soft switch to associate the session, the Bye message is used by the terminal for requesting the soft switch to terminate the session, the Ack message is used by the terminal for reporting the response from the soft switch, the Cancel message is used by the soft switch and/or the terminal for canceling the present procedure, and the Option message is used by the soft switch for requesting capability information from the terminal.
The soft switch checks the link status of the VoIP terminal and maintains the network system stability by performing an appropriate call processing procedure. In order for the soft switch to acquire the link state of the VoIP terminal, the SIP based Register message is used. That is, upon turning on, the VoIP terminal transmits the Register message, and the soft switch receives the Register message and checks the link state of the VoIP terminal. Sequentially, upon receiving the Invite message having the terminal information, such as the transmitter and receiver IP addresses, and Call ID from one of the registered VoIP terminals, the soft switch responsively transmits a 200 OK message to establish the call, register the Call ID, and transmit a Call message to the receiver terminal, whereby an RTP session is established between the transmitter terminal and the receiver terminal, resulting in entrance of a communication (busy state).
The soft switch receives the Register messages from respective terminals periodically so as to check the link states of the terminals. Since the soft switch checks the link state using the Register message in a busy state, the register message can be used as basic information for utilization charges. Also, the link state between the terminal and the soft switch is checked using the Register message such that it is possible to check the Death/Idle and Busy states to perform network management, calculate utilization charges, and effect processing for a new call.
Even though the soft switch can manage the call phase of the terminal in cases of the normal establishment and relief through the communication link between the terminals, it is impossible for the soft switch to manage the call phase in realtime when there is a message loss due to the abrupt impact of the terminal and network problems.
Also, the soft switch receives the register messages from many terminals in a unit time and must process the Invite messages in realtime such that the traffic load increases in proportion to the number of the registered terminals, resulting in a reduction of service quality.
Also, since the terminal must transmit the Register message to the soft switch periodically, e.g. every hour, the soft switch can not acquire the terminal status during the intermediate time between the register messages transmissions.
Recently, Wireless LAN (WLAN) technology-integrated handheld phones have been adopted for use as VoIP terminals. Such portable VoIP terminals have been represented by WiFi Phones based on the WLAN and have been developed in other local wireless networks such as Zigbee, UWB, Bluetooth, etc. All of the WiFi, Zigbee, UWB, and Bluetooth phones, etc. can be called mobile terminals.
The mobile terminals transmit the SIP message to the soft switch through an Access Point (AP) providing the access service using at least one of competition or non-competition media access control schemes to establish the connection to the counterpart mobile or fixed terminal. The procedure in which the AP provides the terminal with the media access service to establish the link to the counterpart terminal has been omitted to simplify the explanation.
That is, the mobile terminal transmits the Invite message to the soft switch and the soft switch transmits the invite message to the counterpart mobile terminal. In response to the Invite message, the receive mobile terminal transmits the 200 OK message to the mobile terminal via the soft switch such that the RTP session is established between the mobile terminals so as to communicate each other.
However, if one of transmit and receive mobile terminals crashes so as to be in an abnormal state during the communication, the communication link between the mobile terminals via the soft switch is broken. Even though the crashed mobile terminal can not transmit the Bye message to the soft switch, the soft switch regards the state of the crashed mobile as the busy state before receiving the Register message. Accordingly, even though the communication link to the crashed mobile terminal has been broken, the utilization charge is unfairly imposed.
Also, even when the communication link between the mobile terminals is broken due to the termination of the RTP session caused by problems of the network equipment or AP, the soft switch maintains the state of the terminal as busy until receiving the Register message since it doesn't receive the Bye message. Accordingly, the soft switch can not process a new call when receiving the Invite message from another terminal even when the previous communication link has been broken, and continues charging the utilization cost until receiving the Register message, resulting in an overcharge.